Zcash activates NU7 with 25-second block target and fee reserve

Zcash activated its NU7 network upgrade at mainnet block 3,543,405, changing the proof-of-work chain’s target block interval from 75 seconds to 25 seconds and routing most transaction fees into a protocol-controlled reserve.

ZecStats, an attributable live chain tracker, recorded the activation block at 02:34 UTC on November 6. The Zcash Foundation’s node release and the NU7 deployment specification independently set the same activation height. The event matters because the new rules affect confirmation cadence, miner compensation, wallet compatibility and the spendability of the network’s oldest shielded pool. It does not, by itself, prove faster observed confirmations, higher use or stronger privacy.

Faster blocks are a target, not a guarantee

ZIP 218 changes the target spacing used by the difficulty adjustment algorithm. A 25-second target means blocks should arrive three times as frequently on average after difficulty adapts, but proof-of-work block times vary. Wallets and exchanges can also require multiple confirmations, so the upgrade does not promise that a payment will settle in exactly 25 seconds.

To keep scheduled issuance approximately unchanged per day, the per-block subsidy falls from 1.5625 ZEC to 0.52083333 ZEC while the number of targeted daily blocks triples. The protocol’s 21 million ZEC cap remains unchanged, and the block count between remaining halvings expands to preserve roughly the same calendar schedule.

The upgrade also introduces global and pool-specific limits on shielded actions. ZIP 218 estimates that the rules raise the Orchard protocol’s throughput ceiling from 2.9 to 6.6 transactions per second while reducing worst-case light-wallet synchronization bandwidth by 37%. Those are specification estimates and adversarial-load models, not measurements of post-activation traffic or wallet performance. More frequent blocks can also increase stale-block and short-fork risk, so live network behavior still needs observation.

Transaction fees now feed a future subsidy reserve

Under NU7, 60% of the aggregate transaction fees in each block are removed from circulation, rounded down, while miners retain the remainder. The Network Sustainability Mechanism records that amount in public consensus state for later reissuance through block rewards.

The deployment specification sets mainnet reissuance to begin at block 8,939,664, which the project expects after the next halving period. The reserve is therefore not a permanent burn and not a discretionary treasury. Its future release is determined by consensus rules, and the supply cap does not increase because reissued ZEC must previously have been removed from circulation or left unclaimed under the specified mechanism.

That design changes fee economics immediately, but current Zcash fees are small and the upgrade provides no evidence that the reserve will eventually supply enough miner revenue to secure the chain as ordinary subsidies decline. That remains an economic hypothesis to test over years.

Version 4 transactions and Sprout stop working

NU7 makes every version 4 transaction invalid. Because the legacy Sprout shielded pool has no supported transaction format beyond version 4, its remaining funds became unspendable at activation. ZecStats measured 12,224.21 ZEC in Sprout at 12:07 UTC on November 6; that is a time-specific chain balance, not a dollar valuation, and the coins are frozen rather than destroyed.

The restriction also reaches version 4 transparent-only and Sapling transactions. Version 5 and version 6 formats remain valid, although transactions signed for the prior consensus branch do not automatically carry across the upgrade. Node operators needed NU7-compatible software to remain on the upgraded chain.

The verified result is a live consensus change, not a verdict on Zcash adoption or price. The next useful evidence will be observed block intervals over a defined sample, stale-block behavior, wallet compatibility reports, transaction demand and the fee reserve’s growth.